This invention relates to a method of making glass (e.g., grey or dark in color) using a technique where selenium (Se) burnoff is reduced during the process of manufacture so as to reduce pollution. The resulting glass compositions are thus useful, for example, in vehicle windows and/or architectural applications.
Privacy windows for use in automobiles and/or architectural applications are becoming more popular, as is demand for grey glass in general. These glasses are typically based upon a standard soda-lime-silica glass composition (used to make float glass) to which is added various colorants to attain the desired coloring and spectral properties. Iron, typically including both ferric (Fe3+) and ferrous (Fe2+) iron, is often used in such glasses. Ferric iron is a strong ultraviolet (UV) absorber and yellow/green colorant while ferrous iron is a known infrared (IR) absorber and blue colorant. Other colorants which are often used in such glasses include Se, Co, Cr, Mn, V, Ce, Ti, Mo, and the like.
Commonly owned U.S. Pat. No. 5,932,502 (hereby incorporated herein by reference) discloses a dark grey privacy glass composition including a colorant portion of Fe2O3 (total iron), Co3O4, Se, and Cr2O3. The resulting glass of the ""502 patent has good coloring and spectral characteristics.
Unfortunately, when making the glass of the ""502 patent a large percentage of the Se originally added to the batch burns off during the process of glass manufacture (i.e., a high rate of Se burnoff is experienced). Se is a known pollutant, and high rates of Se burnoff are thus undesirable for environmental reasons. For example, when making glass according to the ""502 patent commercially, about 0.1000% (wt. %) metallic Se is originally provided in the batch along with about 1.0% salt cake which is used as a refining agent. After the batch is melted and processed, the resulting glass has only about 0.0026-0.0028% Se left therein (the rest of the Se has burned off). This translates into a Se retention of less than 10% (i.e., at least about 90% of the Se originally present in the batch burns off during the process of manufacture). This high rate/percentage of Se burnoff is undesirable.
U.S. Pat. No. 5,346,867 discusses the problem of Se vaporization. In response to the problem, the ""867 patent uses manganese oxide in order to decrease Se burnoff. Unfortunately, the MnO2 technique used in the ""867 patent only enables up to 22.3% of the originally presented Se to be retained (see Table III in the ""867 patent).
In view of the above, it will be apparent to those skilled in the art that there exists a need in the art for a method of making Se-inclusive glass wherein the rate and/or percentage of Se burnoff during the process of glass manufacture can be reduced and/or minimized.
An object of this invention is to provide a method of making a selenium (Se) inclusive glass in a manner such that Se burnoff during the process of manufacture is reduced. This method may be applied to grey colored glass in certain embodiments of this invention, as well as to other colored glasses in other embodiments of this invention.
Another object of this invention is to reduce Se burnoff in a process of glass manufacture by using Epsom salt(s) (e.g., MgSO4xc3x977H2O) as a refining agent and/or melting aide. Surprisingly, it has been found that the use of Epsom salt(s) (e.g., instead of and/or in addition to salt cake or the like) as a batch component enables more Se to be retained (i.e., less Se burnoff).
Another object is to fulfill one or more of the above-listed objects and/or needs.
Generally speaking, this invention fulfills one or more of the above-listed objects or needs by providing a method of making glass, the method comprising:
processing a molten glass batch including Se in order to form a resulting glass product comprising SiO2 and Se, in a manner so that the resulting glass product retains at least 30% of the Se originally present prior to melting.
In other embodiments of this invention, one or more of the above-listed needs and/or objects is/are fulfilled by providing a method of making glass, the method comprising:
providing a glass batch including SiO2, Fe2O3, Epsom salt, and an original amount of Se; and
forming a resulting glass product from the glass batch in a manner such that the resulting glass product includes at least 30% of the original amount of Se due at least to the presence of a sufficient quantity of the Epsom salt in the batch.
In certain other embodiments of this invention, one or more of the above-listed needs or objects is fulfilled by providing a method of making a grey colored glass, the method comprising:
providing a molten glass batch comprising SiO2, Se, and Epsom salt;
processing the glass batch in order to make a resulting grey colored glass product, the grey colored glass product including a base glass portion comprising:
and a colorant portion comprising:
wherein the Epsom salt is provided in the glass batch in sufficient quantity so that the resulting glass product retains at least 30% of the Se originally present in the batch.
Certain other embodiments of this invention fulfill a desired need by providing a grey colored glass comprising:
a base portion and a colorant portion;
said base portion of the glass comprising:
and said colorant portion consisting essentially of:
wherein the glass is grey in color and has a dominant wavelength in the range of from 435 nm to 570 nm, is substantially free of manganese dioxide, and is substantially free of nickel.
Glasses (e.g., colored grey or any other suitable color) according to different embodiments of this invention may be used, for example, in the automotive industry (e.g., windshields, backlites, side windows, etc.), in architectural applications, and/or in other suitable applications. Resulting glass products herein may be from about 1-12 mm thick in different embodiments.
Certain glasses according to this invention utilize soda-lime-silica flat glass as their base composition/glass, to which is added certain ingredients making up a colorant portion. An exemplary soda-lime-silica base glass according to certain embodiments of this invention, on a weight percentage (wt. %) basis, includes the following basic ingredients:
In certain embodiments, for example, glass herein may be made from batch raw materials silica sand, soda ash, dolomite, limestone, with the use of at least Epsom salt(s) as refining agent and/or melting aide. Other minor ingredients, including various conventional refining aids may also be included in the base glass. Additionally, in certain embodiments a spectral modifier such as sodium phosphate (Na2HPO4) in an amount of from 0 to 2.0%, more preferably from 0 to 1.5%, may be added to the batch for color adjustment purposes. Sodium phosphate, while a color modifier, is not defined as a xe2x80x9ccolorantxe2x80x9d herein.
As explained in more detail below, the use of Epsom salts (e.g., MgSO4xc3x977H2O) in the process of glass manufacture has surprisingly been found to reduce Se burnoff during the manufacturing process (e.g., conventional melt and float processing). This reduction in selenium (Se) burnoff is significant in that it both reduces pollution and/or reduces the amount of costly Se that has to be added to the glass batch prior to or during the melt in order to end up with the same amount of Se in the resulting glass composition.
Reducing agent(s) such as Si (metallic), Si, silicon monoxide, SiO, sucrose, and/or carbon may also be used. In other embodiments of this invention, no reducing agent is needed due to the rather high iron content to be discussed more fully below. In certain embodiments of this invention soda-lime-silica based glasses include by weight from about 10-15% Na2O and from about 6-12% CaO. While a soda-lime-silica base glass set forth above is preferred in certain embodiments of this invention, this invention is not so limited. Thus, other base glasses (e.g., borosilicate glass) may instead be employed in alternative embodiments.
In one example embodiment of this invention, to the base glass (e.g., see Table 1 above) a colorant portion is added which causes the resulting glass to be grey in color (i.e., dominant wavelength of from 435 nm to 570 nm). In this embodiment, the resulting grey glass has a dominant wavelength of from 480 nm xe2x88x92560 nm (nanometers), and an excitation purity (Pe) no greater than 11%, more preferably no greater than 8%, and most preferably from 1 to 7%. In this embodiment, an exemplary colorant portion that is added to the base glass is substantially free of cerium, manganese dioxide, and/or nickel (i.e., no more than 0.0030% Ce, CeO, and/or CeO2, no more than 0.0030% Mn or MnO2, and/or no more than 0.0010% Ni and/or NiO), and is characterized as set forth in Table 2 below (in terms of weight percentage of the total glass composition):
In certain embodiments of this invention, the colorant portion is substantially free of other colorants (other than potentially trace amounts). As can be seen above, the colorant portion may also be substantially free of chromium oxide, phosphates, and/or titanium oxide in certain embodiments of this invention. However, in other embodiments chromium oxide may be used to affect color. In certain embodiments, the colorant portion consists essentially of the colorants listed in Table 2 above, while in other embodiments the colorant portion simply comprises or includes the colorants listed in Table 2 above. However, it should be appreciated that small amounts of other materials (e.g., refining aids, melting aids, and/or impurities) may be present in the glass such as manganese, molybdenum, tin, chlorine, zinc, zirconium, Si, sulfur, fluorine, lithium and strontium, without taking away from the purpose(s) and/or goal(s) of the grey glass embodiment of the instant invention. Those of skill in the art will recognized that the aforesaid colorant portion is provided for purposes of example only, and certain embodiments of the instant invention are not so limited.
In preferred embodiments of this invention, Epsom salt(s) (e.g., MgSO4xc3x977H2O) is added to the batch (e.g., including the base glass and colorant portion in Tables 1 and 2 above) prior and/or during the melt in order to reduce Se burnoff. In one example embodiment of this invention, from about 0.1 to 2.0% (wt. %) Epsom salt(s) is added to the batch, and in more preferred embodiments from about 0.2 to 1.5% Epsom salt(s) is added to the batch. As a result of the addition of Epsom salt(s) to the batch, at least about 30% of the original Se added to the batch is retained in the final glass composition, more preferably at least about 40% of the original Se added to the batch is retained in the final glass composition, and most preferably at least about 50% of the original Se added to the batch is retained in the final glass composition. Another advantage associated with Epsom salts is that they do not require a reducing agent to be used in conjunction therewith (although one may be used), which again can help reduce Se burnoff.
Selenium (Se) may be added to the batch in a variety of different forms in different embodiments of this invention. For example, Se may be added to the batch in the form of sodium and/or calcium selenites, iron and/or cobalt selenides, metallic Se powder, or in any other suitable manner. Example Se powder amounts and sodium selenite amounts are shown above in Table 2. While Se often combines with iron as iron selenide (FeSe) in glass to produce brown color, and does so in certain embodiments of this invention, selenium is referred to in the colorant portion herein as xe2x80x9cSexe2x80x9d which is meant to include, for example, its state as Se as well as its other state(s) in glass such as FeSe (and all Se valence states). For example, Se may exist in the form of selenates, selenides, selenites, polyselenides, and/or in elemental form.
Referring to Table 2 above for example, in more preferred embodiments of this invention Se can be added to the batch as a colorant in either (a) the form of metallic Se powder, and/or (b) the form of Na2SeO3. If added in the form of metallic Se powder, from about 30-90 ppm (parts-per-million) is added to the batch. However, if added in the form of Na2SeO3, then from about 70-180 ppm of Na2SeO3 is added. As will be appreciated by those skilled in the art, 60 ppm Se metallic powder has about the same amount of Se as does 144 ppm Na2SeO3. A combination of Se metallic powder and Na2SeO3 may be added in alternative embodiments of this invention. As can be seen from the chart/table below, the addition of Se in the form of Na2SeO3 helps Se retention even more in certain embodiments of this invention.
Regarding cobalt (Co), this blue colorant may be added to the glass batch in the amounts set forth in Table 2 above in certain example embodiments. Moreover, it is believed that much of the cobalt in the glass is in the oxide state of Co3O4. However, other oxide states of CoO are also possible in glasses according to this invention. Thus, unless expressly stated to the contrary, the terms xe2x80x9cCoOxe2x80x9d and xe2x80x9cCo3O4xe2x80x9d as used herein include not only cobalt in this/these particular oxide state(s), but also include(s) cobalt which may be present in other oxidation state(s).
The total amount of iron present in the glass is expressed herein in terms of Fe2O3 in accordance with standard practice. This, however, does not imply that all iron is actually in the from of Fe2O3. Likewise, the amount of iron in the ferrous state is reported herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO. The proportion of the total iron in the ferrous state (i.e., FeO) is used to determine the redox state of the glass, and is expressed as the ratio FeO/Fe2O3 which is the weight percentage (%) of iron in the ferrous state (expressed as FeO) divided by the weight percentage (%) of total iron (expressed as Fe2O3). Thus, Fe2O3 herein means total iron and FeO means iron in the ferrous state. According to certain embodiments of this invention, the colorant portion of the glass composition herein is characterized by a redox value (i.e., FeO/Fe2O3) of from 0.20 to 0.30, more preferably from 0.23 to 0.27.
Optionally, titanium oxide may be used in certain embodiments of this invention to increase IR absorption. Moreover, the use of titanium oxide may enable the reduction and/or elimination of chromium oxide from the composition. Additionally, it is believed that the titanium oxide may also help retain Se in the glass (i.e., reduce Se burnoff) by causing it to be more evenly distributed throughout the melt.
It is noted that glass according to this invention is often made via the known float processing in which a tin bath is utilized. It will thus be appreciated by those skilled in the art that as a result of forming the glass on molten tin in certain exemplary embodiments, small amounts of tin or tin oxide may migrate into surface areas of the glass on the side that was in contact with the tin bath during manufacture (i.e., typically, float glass may have a tin oxide concentration of 0.05% or more (wt.) in the first few microns below the surface that was in contact with the tin bath).
When used in the automotive market, grey glasses according to certain embodiments of this invention (e.g., at about 4 mm thickness for purposes of reference) may have an Lta (visible transmission, Ill. A, 2 degree observer) of from 10-30%, more preferably from 12-24%, most preferably from 13-20%; an IR transmission percentage (%) of from 3-28%, more preferably from 4-24%, and most preferably from 8-21%. With regard to transmissive color, these grey glasses according to certain embodiments of this invention may have an a* value (Ill. D65, 10 degree observer) of from 0.0 to xe2x88x9210.0, more preferably from xe2x88x922.0 to xe2x88x928.0, and most preferably from xe2x88x923.0 to xe2x88x927.0; and a b* value (Ill. D65, 10 degree observer) of from xe2x88x924.0 to +10.0, more preferably from 0 to +9.0, and most preferably from +2.0 to +8.0. Herein, transmissive Lta is measured in terms of Ill. A, 2 degree observer, while a* and b* color values are measured in terms of Ill. D65, 10 degree observer.
The above-listed colorant portion(s) data and base glass data are for purposes of example only, and the instant invention is not so limited. Instead, one focus of the instant invention is the reduction of Se burnoff during the glass manufacture process, and the use of Epsom salts in a Se inclusive batch may be used in accordance with this invention in combination with base glasses and/or colorant portions other than those discussed above.